1. Field of the Invention
The present invention relates to a wear leveling method. More particularly, the present invention relates to a wear leveling method for a non-volatile memory and a controller using the same.
2. Description of Related Art
With a quick developing of digital camera, cell phone camera and MP3, demand of storage media by customers is increased greatly. Since a flash memory has the advantages of non-volatile, energy saving, small size and none mechanical structure etc., it is suitable for portable applications, and especially for portable battery-powered products. Besides a demand of built-in memories of the portable products, demand of the flash memories used for external products such as small memory cards and flash drives is increased greatly in the market, since a user may simultaneously own a plurality of the memory cards and the flash drives. Therefore, the flash drive industry becomes a hot industry within the electronics industry recently.
Though the flash drive has the advantages of programmable, erasable, data saving after power-off, erase times of blocks within the flash memory are limited. For example, the blocks in the flash memory may be worn after being erased 10,000 times. Data loss may be caused when the storage capacity or performance of a flash memory is obviously deteriorated by its worn-out blocks.
Wearing of the flash memory blocks is determined by the number of times this block is programmed or erased. In other words, the wear of a block is relatively low if the block is programmed (or written) only once; contrarily, the wear of a block is relatively higher if the block is programmed and erased repeatedly. For example, when a host keeps writing data into a flash memory by using the same logical block address (LBA), the block having the corresponding physical block address (PBA) in the flash memory is then repeatedly written and erased.
Generally speaking, the existence of worn-out blocks will reduce the performance of a flash memory even if the wear of other blocks are still relatively low. Besides the deterioration in the performance of the worn-out blocks, the performance of the entire flash memory is also reduced when the good blocks cannot provide enough space for storing data. In other words, when the number of worn-out blocks in a flash memory exceeds a threshold value, the flash memory is considered unusable even there are still good blocks. In this case, those good blocks are wasted.
To prolong a lifespan of the flash drive, utilization of the blocks in the flash drive should be leveled. Generally, the blocks of the flash drive are grouped into a data area and a spare area. According to a conventional wear leveling method, when the flash drive is operated for a period of time, the blocks within the data area and the blocks within the spare area are logically exchanged sequentially, hopefully the blocks with lesser erase times may be exchanged to the data area for being programmed (or written). However, such method for logically exchanging the blocks within the data area sequentially to the blocks within the spare area cannot ensure the exchanged blocks are those with lesser erase times, and if the exchanged blocks are those with greater erase times, wearing of the blocks may be accelerated, and therefore an effect of the conventional wear leveling method is limited.
Accordingly, a novel wear leveling method is required to effectively prolong the lifespan of the flash drive.